We will develop a new x-ray spectrometer, based on novel high efficiency silicon x-ray detectors; with good energy resolution and high count rate capability for synchrotron x-ray fluorescence (XRF) applications. In Phase I, we extended the very successful silicon drift detector design, currently fabricated on thin 0.3 mm thick substrates, into the realm of thick detectors (up to 1.5 mm thick). This added thickness is critical in extending the x-ray absorption capability of the detectors from 15 keV to 40 keV. Synchrotron XRF techniques are becoming essential tools for biological, chemical and materials analysis. Third generation synchrotrons, such as the Advanced Photon Source (APS), have photon flux brilliance in the 6-40 keV region that allow efficient x-ray fluorescence analysis with probe sizes of a micrometer and below. All of these beam-lines require high-count rate, good energy resolution energy dispersive x-ray detectors that have efficient absorption up to 40 keV. The new, thicker drift detectors will have the advantages of non-cryogenic cooling, good energy resolution, and an order of magnitude improvement in count rates compared with conventional silicon and germanium XRF detectors, while providing a significant increase in efficiency above 10 keV. The Phase II work will include the optimization of the thick detector prototypes including increase in area from 20 mm2 to 50 mm2; improve the yield and design of the process for transfer to a commercial silicon foundry. The detectors will be evaluated with respect to noise, energy resolution, and efficiency and count rate capability in response to x-rays in the 5-60 keV range. The best devices will be selected to be incorporated into a three-channel x-ray spectrometer. The spectrometer will be custom-designed and evaluated in a hard x-ray microprobe application at the Advanced Photon Source at Argonne National Laboratory, in collaboration with APS staff. The commercial applications for such high efficiency spectrometers include chemical analysis in steel, materials, chemical, geological and biological applications.